1. Field of the Invention
The present invention relates generally to a marine outboard drive, and more particularly to a marine engine.
2. Description of Related Art
The reciprocating movement of the crankshaft, pistons and rods in a convention internal combustion marine engine commonly generates certain forces and vibrations which detrimentally affect the operation of the engine. It is well known that these forces should be balanced in order to provide smooth running of the engine.
Some prior marine engine designs have used crankshafts with large counterweights to dampen or cancel the vibrational forces produced by crankshaft, piston, and rod movement. Large counterweights, however, require a large crank chamber which increases the external size of crankcase and the girth of the engine.
Other marine engines have used one or more balancer shafts driven by the engine crankshaft. Such shafts commonly include eccentric masses and have lengths which are coextensive with the length of the crankshaft. These balancer shafts often extend along the sides of the cylinder block. Although effective in dampening the vibrational forces produced by the reciprocating motion of the engine, the addition of further shafts to the engine shaft previously has complicated and enlarged the overall construction of the engine.
An enlarged engine size tends to increase drag on the watercraft, especially with an outboard motor. This is because the power head, which includes the engine, conventionally extends well above the transom of the watercraft, and a larger sized power head produces more drag on the watercraft. Increased drag of course affects the performance of the watercraft.